1. Field of the Invention
The present invention relates to an information detection display more particularly, to an information detection display that includes a light sensing unit.
2. Description of the Related Art
A liquid crystal display includes substrates on which pixel electrodes and a common electrode are formed, and a liquid crystal layer disposed between the substrates. The pixel electrodes are disposed on one of the substrates as a matrix. Each pixel electrode is connected to a switching element, such as a thin film transistor (TFT), which applies data voltages to the pixel electrode. The common electrode is formed on the opposite substrate, on which the pixel electrodes are not formed, and has a common voltage. The common electrode faces the pixel electrodes, creating a liquid capacitor with the liquid crystal layer disposed between the electrodes. The liquid capacitor and the switching elements connected to each pixel form unit pixel, and the plurality of unit pixels are disposed as matrix.
An information detection display is a display that can detect position information or touch information from, for example, a finger or stylus applied to the surface of the display.
The position information or touch information of a selected position in a predetermined area of such an information detection display is detected by detecting a variation in resistance or light. When resistance is used to detect position information, a plurality of resistive lines are disposed on the lower and upper substrates, and extend vertically or horizontally. The resistive lines contact each other as a result of external stimulus, for instance a touch to the surface of the display, and vary the resistance thereof. The device senses the variation of the resistance to find the position or touch information. On the other hand, when light is used, light sensing units that can sense variations in the amount of light, or amount of light having a predetermined wavelength, are used to detect the position information or the touch information.
A device using the resistive method is usually formed on a transparent substrate and can be easily combined with other display devices. However, the resistive method decreases the luminance of the display device, and increases the thickness of the product. On the other hand, a device using the light sensing method usually includes light sensing units incorporated into the display device, and such light sensing units typically do not increase the thickness of the device. Thus, research is ongoing on devices that utilize the light sensing method.
When light sensing units are incorporated into a display device, the light sensing units can be affected by other components of display device. For example, the light sensing unit is affected by extraneous light, variations in temperature, and also applied bias voltage. Particularly, bias voltage applied to the light sensing unit can change the threshold voltage of the thin film transistor. The change in threshold voltage affects a number of characteristic of thin film transistors included in the light sensing unit, which can affect the performance of the device.